An intelligence quotient (IQ) is a total score derived from one of several standardized tests designed to assess human intelligence. The abbreviation "IQ" was coined by the psychologist William Stern for the German term Intelligenzquotient, his term for a scoring method for intelligence tests he advocated in a 1912 book.When current IQ tests are developed, the median raw score of the norming sample is defined as IQ 100 and scores each standard deviation up or down are defined as 15 IQ points greater or less, although this was not always so historically.
IQ scores are used for educational placement, assessment of intellectual disability, and evaluating job applicants. Even when students improve their scores on standardized tests, they don't always improve their cognitive abilities, such as memory, attention and speed.In research contexts they have been studied as predictors of job performance, and income. They are also used to study distributions of psychometric intelligence in populations and the correlations between it and other variables.